Method for Processing Solid and Liquid Wastes from the Production of Vegetable Oil

ABSTRACT

A method for processing solid, organic wastes obtained in the production of vegetable oil, for example the production of palm oil, chiefly consisting of pressing residues of the oil plants and/or oil seeds and oil-containing waste water by hydrothermal carbonization (HTC), wherein the oil present in the waste water in emulsified form is sorbed by the solids rich in carbon, which are obtained from the solid wastes.

FIELD OF THE INVENTION

This invention relates to a method for processing solid, organic wastes obtained in the production of vegetable oil, chiefly consisting of pressing residues of the oil fruits and/or oil seeds, and of oil-containing waste water. This invention furthermore relates to the advantageous use of products of the method according to the invention in the cultivation of oil palms, and for energy generation. In particular, the invention is suitable for use in the production of palm oil.

PRIOR ART

To satisfy the demand for fuel from renewable raw materials, such as biodiesel, large palm oil plantations have been established in the last few years, especially in Malaysia and Indonesia. What is problematic in this development, beside the loss of primeval forest areas for establishing these plantations, is the large amount of solid and liquid waste obtained in the palm oil production.

When pressing out the palm oil in the oil mill, about 1.2 t of pressing residues are left per ton of palm oil produced, consisting of fruit fibers and palm seed husks, so-called Empty Fruit Bunches (EFB).

Due to water washing of the palm oil pressed out in the oil mill, about 3 to 4 m³ of waste water per ton of palm oil produced are obtained at the same time, so-called Palm Oil Mill Effluent (POME). The waste water obtained is loaded with organic constituents, such as oil, fatty acids and carbohydrates. The problem is that the organic constituents form a stable oil/water emulsion with the water, which complicates the further treatment of water.

The solid wastes usually are burnt for generating energy for the oil mill, which involves strong smoke development and therefore is a great burden for man and the environment.

The waste water from the oil production is collected in waste water ponds. The organic substances in part are biodegraded anaerobically, which beside a strong odor nuisance by sewer gases leads to the formation of the gases carbon dioxide and methane, which are harmful to the climate. To avoid these disadvantages, the smoke development during the combustion of the solid wastes and the environmental impact of the biological waste water clarification, F. Schuchardt describes a method in which the treatment of the waste water by anaerobic, biological reactions is carried out in a fermentation reactor, so that the resulting gases carbon dioxide and methane can be trapped and be utilized in a climate-friendly manner. The waste water thus purified then is mixed with the biological solid wastes in compost heaps and composted to fertilizer. What is important for this method is the use of a special high-performance fermenter or a fixed-bed reactor and for the operation of the compost heaps the use of a special turning machine for the intensive mixing of the compost; F. Schuchardt, Bundesforschungsanstalt für Landwirtschaft, Forschungs-Report 2/2007; Dr. F. Schuchardt, Bio-Solar Biogas-Fachtagung “Regenerative Energie vom Bauernhof”, May 2, 2003 in Heiden; M. Bockisch, Fats and Oils Handbook, AOCS Press, 1993.

DESCRIPTION OF THE INVENTION

While by methods according to the prior art the wastes are converted into compost and biogas, an alternative method should be provided by the present invention, which converts the wastes into water containing nutrients, which is suitable for watering the oil plant plantation, and a carbonaceous solid fuel, which e.g mixed with heating oil, is suitable for energy generation by combustion.

The object is solved by a method according to the characterizing part of claim 1 in cooperation with the features of its generic part. Further advantageous aspects of the invention can be taken from the sub-claims. In the method according to the invention, the solid organic wastes are comminuted and in a stirred, heated reactor mixed with the waste water to form a suspension, the pH value of the suspension is adjusted in the acid range, the atmospheric oxygen is removed from the reactor by flushing with inert gas and the reactor is closed air- and pressure-tight, and the suspension is heated to at least 170° C. and kept at elevated pressure for at least 0.5 hours, wherein the solid, organic wastes chiefly are converted to a solid material rich in carbon, and wherein the oil originally contained in the waste water is sorbed by the obtained solid material rich in carbon, and wherein subsequently the suspension is cooled, removed from the reactor and separated into a coal and a waste water fraction.

The conversion of biomass into solid products rich in carbon, for example coal or coal precursors such as humus, peat and lignite, is known under the term “Hydrothermal Carbonization” or “HTC” and described in the specialist article “Zauberkohle aus dem Dampfkochtopf”, Max Planck Forschung 2/2006, pages 20-25 and in the document WO 2008/113309. An advantage of this method consists in that biomass is converted into coal or its precursors peat, humus, lignite, without carbonaceous waste gases such as carbon dioxide or methane being produced. As the only waste product water is obtained, which possibly still contains dissolved by-products of the HTC reaction.

In the present case of application, the processing of solid and liquid waste substances of the production of vegetable oil, to be observed by way of example in the production of palm oil, it is however not obvious to use the hydrothermal carbonization, since here water and biomass are not present as separate starting substances, as described in the prior art of the HTC process, but an extremely stable oil/water emulsion and the pressing residues of the oil fruits and/or oil seeds are available as biomass to be used.

As our own experiments have shown, the oil/water emulsion is so stable that it cannot be broken by usual measures such as the addition of surfactants, boiling, acidifying to a pH value of 2, centrifuging or the addition of activated carbon. The reason for the high stability of this emulsion probably are the free fatty acids and glycerides likewise present in the waste water, among them in particular the monoglycerides, which represent very effective emulsifiers. Accordingly, it could not be expected that the emulsion would be broken by the HTC process and hence the one important problem of this waste processing, the treatment of the waste water loaded by the oil/water emulsion, would be solved.

Contrary to this assumption, the experiments however have led to the surprising result that by the HTC process the waste water of the palm oil production, which is loaded with organic impurities, is converted into an oil-free water advantageously loaded with the salts and minerals originating from the plant remains, which water is quite suitable for watering the palm oil plantations. The oil originally contained in the loaded waste water is sorbed by the solids rich in carbon obtained from the plant remains. While carrying out the HTC process, the splitting of the emulsion obviously is effected by the chemical and/or biological processes during the conversion of the biomass into coal.

The fundamental and well-known chemical processes of the HTC process consist in that hydrogen and oxygen atoms are extracted from the compounds in which they are present in the biomass, e.g. glucose, and combine to H₂O. In order to not impair these chemical processes, the process must must be carried out under exclusion of air. Residue air must be removed from the reactor by flushing with inert gas before heating the suspension. The energy balance of these chemical processes on the whole is positive, but the concrete height of the energy gain of course depends on the kind of biomass used. Beside the energy balance of the chemical processes, however, the energy balance of the technical processes of the method must also be observed. For example, much heating energy is required, because the HTC process only proceeds with economic speed above 170° C. In addition, because of the high temperature level at which the HTC process takes place, a good heat insulation of the reactors is required.

To operate the process uniformly and with a high conversion rate of the biomass, energy also is required for constantly intermixing the feedstocks. To economically operate the HTC process, it is also important to use the energy produced by the chemical processes for heating to the maximum possible extent. Therefore, it is recommendable in principle to operate the process with several reactors in parallel offset in time and with a common heating system. The process in principle can be carried out both intermittently and continuously or semicontinuously, wherein in the two last-mentioned cases suitable measures must be taken for supplying the educts and for discharging the products.

Preferred Aspects of the Invention

To create a sufficiently large surface of the solid particles for the economic conversion of the solid wastes from the production of vegetable oil, it is advantageous to comminute the solid organic wastes to a suitable particle size, before mixing the same into the waste water loaded with organic impurities. In the case of the application of the method in the production of palm oil, a particle size of 2 to 5 cm was found to be particularly suitable.

To be able to provide sufficient thermal energy for maintaining the process temperature of at least 170° C., it is advantageous to adjust the dry matter content of the suspension before heating to 10 to 40%.

The chemical processes of the HTC process proceed at an accelerated rate in an acidic environment. Therefore, the pH value of the suspension before heating advantageously should be adjusted to a value between 3.0 and 6.9, preferably to 3.0 to 3.5. However, it is required to neutralize the oil-free water obtained by the method, before using the same for watering the oil plants. Preferably, KOH is used for this purpose.

To avoid too strong boiling of the suspension in the reactor, which can lead to the soiling of the reactor cover and of measuring and safety valve ports present in the cover, it is advantageous when inside the reactor, prior to heating, an elevated pressure, preferably of 5 to 15 bar, is generated by introducing inert gas.

To allow the HTC process to proceed with economic speed, the adjustment of an elevated operating temperature is required. Too high temperatures on the other hand should be avoided, since they put strain on the apparatuses and fittings used and lead to unnecessary energy losses. Therefore, it is advantageous to carry out the method at an operating temperature between 170 and 320° C.

In dependence on the desired degree of conversion (so-called degree of coalification) of the used solid, biological wastes to peat, humus, lignite and/or hard coal, the residence time of the suspension at operating temperature should be chosen. For the present case of application, in which a fuel should be obtained as product of the process, a maximum possible conversion of the biomass into a solid material rich in carbon, such as coal, is desired. Residence times between 0.5 and 16 hours were found to be advantageous.

At the end of the HTC process, the separation of the suspension into a solid and a waste water fraction is effected by means of mechanical separation methods, preferably the decantation, filtration or centrifugation, or combinations thereof.

A preferred development of the invention consists in the use of the solid product rich in carbon as fuel, which can be used alone or in admixture to other fuels, e.g. as suspension after mixing into heating or heavy oil.

A further preferred development of the invention consists in the use of the treated waste water for watering plants, preferably oil plants, wherein the waste water first is neutralized, preferably with KOH.

INDUSTRIAL APPLICABILITY

The invention provides a method for processing solid and liquid wastes from the production of vegetable oil, which is characterized by its technical simplicity and in which products are obtained, which are unproblematic as regards their disposal or which even can advantageously be reused at the site of the oil plantation. Especially these advantages render the use of the method according to the invention attractive for the palm oil production in tropical countries. 

1. A method for processing solid, organic wastes and waste water obtained in the production of vegetable oil, wherein the solid wastes comprise pressing residues of oil fruits or oil seeds and the waste water contains vegetable oil residues beside other organic impurities, which are present in the waste water in emulsified form, wherein the solid, organic wastes are comminuted and in a stirred, heated reactor mixed with the waste water to form a suspension, the pH value of the suspension is adjusted in the acidic range, the atmospheric oxygen is removed from the reactor by flushing with inert gas, the reactor is closed gas-tight and the suspension is heated to at least 170° C. and kept at elevated pressure for at least 0.5 hours, wherein the solid, organic wastes chiefly are converted to a solid material rich in carbon, and wherein the emulsion of waste water and vegetable oil residues is broken and the oil is sorbed by the obtained solid material rich in carbon, and wherein subsequently the suspension is cooled, removed from the reactor and separated into a solids and a waste water fraction.
 2. The method according to claim 1, wherein the solid, organic wastes are comminuted to a particle size of 2 to 5 cm.
 3. The method according to claim 1 wherein the dry matter content of the suspension before heating is adjusted to 10 to 40%.
 4. The method according to claim 1 wherein the pH value of the suspension, before heating, is adjusted to a value between 3.0 and 6.9.
 5. The method according to claim 1 wherein inside the reactor, before heating, an elevated pressure of 5 to 15 bar is generated by introducing inert gas.
 6. The method according to claim 1 wherein the suspension is heated to and maintained at temperatures between 170 and 320° C.
 7. The method according to claim 1 wherein the suspension is maintained at over 170° C. for a time between 0.5 and 16 hours.
 8. The method according to claim 1 wherein the separation of the suspension into a solids and a waste water fraction is effected by means of mechanical separation methods.
 9. (canceled)
 10. (canceled)
 11. The method according to claim 4 wherein the pH value of the suspension, before heating, is adjusted to a value between 3.0 and 3.5.
 12. The method according to claim 8 wherein the means of mechanical separation is decantation, filtration or centrifugation. 